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Thermophysical property prediction of supercritical multiple mixtures fluid by molecular dynamics simulation

Journal of Molecular Liquids 2025年 432卷

作者： Gui, Tete Li, Jiasunle Ge, Zhiwei Guo, Liejin State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

Supercritical multiple mixtures (H2O/CO2) fluids are produced in the poly-generation system based on supercritical water gasification (SCWG). Understanding the thermophysical property of supercritical multiple mixtures fluid is rather essential to design and industrialize the poly-generation system. At present, the selection of force field models for H2O/CO2 mixtures are rather complicated, chaotic and inconsistent, the calculation of each parameter necessitates the use of one force field model. There is no universal force field model to calculate and conduct thermophysical property of H2O/CO2 at one time in a wide range of temperature within SCW. In this paper, heat capacity, viscosity and thermal conductivity of multiple mixtures in supercritical and near-critical water (575 K–1075 k) are first investigated via a novel common force field model with molecular dynamics (MD) simulations. The effects of different factors including the pressure, temperature and CO2 mass fraction on thermophysical properties of H2O/CO2 at a wide range of temperature were first analyzed and conducted in detail. The calculated results indicate that the phenomenon "critical point drift" for viscosity and thermal conductivity of H2O/CO2 mixtures migrating toward the low temperature region occurs. The drift values of viscosity and thermal conductivity are about 10 K and 28 K. The variation of heat capacity and viscosity of H2O/CO2 mixtures increases with increasing pressures only in low temperatures region (700 K-–800 K), while the thermal conductivity always increases with increasing pressures. When the mass fractions of CO2 increases from 20 % to 40 % and 60 %, the drift values for thermal conductivity and viscosity of H2O/CO2 mixtures decreases from 628 K to 624 K and 620 K, and from 627 K to 618 K and 610 K, respectively, and the peak heat capacity decreases from 64.9 J/mol·K to 52.4 J/mol·K and 45.1 J/mol·K. The fitting polynomial to determine conductivity, viscosity and heat capacity H

关键词： Temperature distribution

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Pattern and Dynamics of Methane/Water Two-Phase flow in Deep-Shale Illite Nanoslits

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SSRN 2024年

作者： Wang, Rui Yang, Xu Li, Gao Zheng, Wenxiu Zou, Zhenhai Sun, Chengzhen State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Shaanxi Xi’an710049 China State Key Laboratory of Oil and Gas Reservoir Geology and Exploration Southwest Petroleum University Sichuan Chengdu610500 China Air and Missile Defense College Air Force Engineering University Shaanxi Xi’an710051 China Wuhan Second Ship Design and Research Institute Wuhan430202 China

Developing deep shale gas is crucial for the sustainable development of unconventional energy sources. Deep shale has a high illite content, and understanding the structure and flow behaviors of methane and water coexisting in deep shale illite nanoslits is essential for methane transport and production in deep shale reservoirs. Here, molecular dynamics simulations were performed to investigate the methane and water flow characteristics in slit-shaped illite nanopores. The effects of water saturation, acceleration, and pore size on two-phase flow are elucidated. The results show that water molecules preferentially adsorb on the surface of the illite channel. As the water saturation increases, the water phase gradually forms a water film, water bridge, and water lock, ultimately creating methane nanobubbles surrounded by the water phase. The existence of the water phase compresses the methane flow space. With increasing water saturation, the peak methane density near the channel wall gradually disappears, and the density distribution curves show parabolic shapes. The methane flow flux decreases with the increase of water saturation, mainly when the water saturation increases from 0% to 40%. In illite slits with pore sizes ranging from 2 to 4 nm, the flow rates of water and methane increase with increased pore size. These results are expected to provide insights into developing deep shale gas reservoirs, such as optimizing hydraulic fracturing design and reliably predicting production performance. © 2024, The Authors. All rights reserved.

关键词： Methane

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Revised control strategy for coal-fired power plants during transient processes considering heat transfer deterioration of cooling wall: Flexibility enhancement and security operation

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International Journal of Heat and Mass Transfer 2025年 251卷

作者： Dengliang Wang Yongliang Zhao Wei Gao Weixiong Chen Chaoyang Wang Junjie Yan State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an 710049 China

The increasing integration of intermittent renewable energy sources has heightened the need for enhanced deep peaking and operational flexibility within thermal power plants. This trend poses an enormous threat to the safe operation of boilers, especially cooling wall, underscoring the critical importance of scrutinizing the thermo-hydraulic performance of cooling walls during transient operations. In this study, a 1100 MW ultra-supercritical thermal power plant is used as the research object. A comprehensive one-dimensional dynamic model of the cooling wall is devised, grounded in fundamental principles encompassing mass conservation, momentum conservation, energy conservation, state, metal heat storage, and heat transfer Equations. The analysis yields temperature distributions of the working fluid, inner wall, and outer wall along the height direction of the cooling wall, unveiling instances of dry-out phenomenon during load cycling processes. The investigation reveals that heat transfer deterioration stands out as a primary factor behind intermittent fluctuations in metal wall temperatures. At load cycling rates of 2.5% Pe/min and 3.0% Pe/min, the maximum temperatures of the metal tube wall during the loading up process surge to 527.9°C and 557.3°C, respectively. Furthermore, a revised control strategy is proposed based on the identified heat transfer deterioration characteristics of the cooling wall. Notably, during the loading up process, the peak wall temperature is substantially curtailed from 557.3°C to 502.2°C at a rate of 3.0% Pe/min. This strategic adjustment results in an augmented maximum power ramp rate, escalating from 2.5% Pe/min to 3.0% Pe/min, upon the adoption of the revised control strategy.

关键词： Fossil fuel power plants

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Thermal Management for the 18650 Lithium-Ion Battery Pack by Immersion Cooling with Fluorinated Liquid

SSRN

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SSRN 2023年

作者： Li, Yang Bai, Minli Zhou, Zhifu Wu, Wei-Tao Hu, Chengzhi Gao, Linsong Liu, Xinyu Li, Yubai Song, Yongchen Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education Dalian University of Technology Dalian116023 China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'An710049 China School of Mechanical Engineering Nanjing University of Science and Technology Nanjing210094 China

In this work, a new battery thermal management system (BTMS) utilizing a SF33-based liquid immersion cooling (LIC) scheme has been proposed. Firstly, the comparative investigation focuses on the temperature response of the LIC and forced air cooling (FAC) modules in different scenarios. The results demonstrate that LIC module effectively mitigates heat accumulation, thereby presenting notable advantages in terms of temperature control and equalization, even though the LIC module works under the stage without phase change occurrence. During 2C and 3C charging, the highest temperatures of the LIC module are observed to be 10 °C and 19.1 °C only lower than those of the FAC module, respectively. Furthermore, the highest temperature differences of the LIC module are only 12.89% and 8.57% of the corresponding values exhibited by the FAC module. Moreover, the associated cooling energy consumption for the LIC module is greatly reduced, amounting to only 16.47% and 43.76% of that required by the FAC module. Subsequently, an active control scheme for the LIC is initially proposed, and the phase change process of the LIC under various discharging rates is recorded and analyzed using a high-speed camera. This study serves as a preliminary proof of concept for the feasibility of SF33-based LIC scheme in BTMS. © 2023, The Authors. All rights reserved.

关键词： Lithium-ion batteries

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General analytical equation of state for nanoconfined gases derived from statistical physics

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Physical Review E 2025年第2期111卷 025413-025413页

作者： Chengzhen Sun Haoxuan Li Zhixiang Zhao Mehdi Neek-Amal Bofeng Bai State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an Shaanxi 710049 China School of Urban Planning and Municipal Engineering Xi'an Polytechnic University Xi'an Shaanxi 710048 China Department of Physics Faculty of Sciences Shahid Rajaee Teacher Training University 16875-163 Lavizan Tehran Islamic Republic of Iran Department of Physics University of Antwerp Groenenborgerlaan 171 2020 Antwerp Belgium

The pressure prediction of nanoconfined gases is crucial for various industrial applications, yet existing equations of state (EOS) often compromise between accuracy and usability. This study derives a theoretical EOS in analytical form, combining precision and practicality through statistical physics. It begins by examining the pressure drop mechanism due to adsorbed molecules and refines molecular pairing and potential energy interactions. The resulting EOS accurately predicts the pressure of gases in nanoconfined spaces, especially with an average prediction error of about 5% for strongly adsorbing gases like nitrogen, oxygen, and argon. Additionally, it aligns with the Van der Waals EOS under macroscopic conditions, offering a unified framework across scales. This model enhances both engineering applications and the understanding of nanoconfined EOS.

关键词： Van der Waals forces

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Investigation of Thermal Radiative Transfer Characteristics of Single Water Droplet

SSRN

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SSRN 2023年

作者： Zhang, Dan Tu, Maoping Yuan, Yang Han, Wei State Key Laboratory of Multiphase Flow in Power Engineering School of Energy & Power Engineering Xi'an Jiaotong University Shaanxi Xi’an710049 China Xi'an Thermal Power Research Institute Co. Ltd Shaanxi Xi’an710054 China

Directly heat water droplet by thermal radiation was the key process of coupling solar energy to achieve green production in many industrial applications, such as desalination, carbon capture, energy storage, and so on. The radiative transfer of single water droplet for given irradiation, including reflection, absorption, transmission and their dependences on external irradiation, droplet geometry and radiative properties were investigated through a calculation model set up according to zone method. In current study, the ranges of equivalent diameter and length-width ratio of droplet were 0.1-1.0 mm, 1-10 respectively, its absorption coefficient was 10-15000 m-1 and refractive index was 1.2-2.0. Results suggested that, (1) the absorption mode of droplet could be classified into surface absorption (SA) and volumetric absorption (VA) depending on whether its optical thickness was greater than 1. In VA, droplet could get uniform and fast temperature increasing, and its absorptivity and mean temperature increase rate could be simultaneously improved by increasing absorption coefficient. (2) Scattering included reflection and transmission. Compared with incident irradiation, reflection distributed mainly on the same side of droplet's long axis, while transmission mainly on the opposite side. The overall reflectivity increased with rising refractive index, but was independent on droplet size. While its transmissivity increased with enlarging length-width ratio or reducing equivalent diameter. (3) In VA, at least 40% of incident irradiation was scattered out. The total quantity of scattering could be adjusted by changing absorption coefficient in VA or refractive index in SA. The proportion of transmission in scattering could always be increased by reducing refractive index. © 2023, The Authors. All rights reserved.

关键词： Drops

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Numerical simulation of condensation of supercritical water gasification products in a supersonic nozzle

International Journal of Fluid Engineering

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International Journal of Fluid Engineering 2024年第4期1卷 76-88页

作者： Hongtu Wu Miso Jurcevic Henrik Ström Muhammad Shahzad Khurram Hui Jin State Key Laboratory of Multiphase Flow in Power Engineering(SKLMF) Xi’an Jiaotong University28 Xianning West RoadXi’an 710049ShaanxiChina LTEF—Laboratory for Thermodynamics and Energy Efficiency Faculty of Electrical EngineeringMechanical Engineering and Naval Architecture(FESB)University of SplitRudjera Boskovica 3221000 SplitCroatia Chalmers University of Technology GöteborgSweden COMSATS LahorePakistan

The clean and efficient separation of supercritical water gasification products(SCWGP)has emerged as a significant challenge in supercritical water gasification *** paper proposes the use of a supersonic nozzle for the condensation and separation of H2and CO_(2)from SCWGP,leveraging the high-pressure characteristics of these *** establishing a flow model and a condensation model for the supersonic nozzle,the effects of inlet pressure and inlet temperature on the condensation process are *** analysis reveals that the latent heat released during condensation causes an abnormal distribution of pressure and temperature within the *** the inlet pressure of the nozzle is increased from 7.0 to 9.0 MPa,the liquid phase mass fraction at the outlet rises from 5.3×10^(-3)to ***,when the inlet temperature is lowered from 300.0 to 290.0 K,the liquid phase mass fraction at the outlet also rises from 5.3×10^(-3)to *** increase in inlet pressure leads to the condensation location shifting toward the throat by~8.5×10^(-3)m·MPa^(-1),while the impact of inlet temperature is approximately-2.3×10^(-3)m·K^(-1).The nucleation rate in the nozzle is always concentrated in a small region.

关键词： condensation separation outlet

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Identification of flow cut-off pattern and prediction of cut-off time of gas-liquid two-phase flow in pipeline-riser system

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Physics of Fluids 2025年第5期37卷

作者： Liu, Tianyu Wang, Hanxuan Zou, Suifeng Du, Yaohua Guo, Liejin State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

For offshore pipeline-riser systems, cyclic flow cut-off in slugging flow pattern should be identified and necessarily mitigated to satisfy the requirement of normal operation of gas-liquid separator. Since conventional studies on flow pattern identification were not directly related to the harmfulness of slugging and the decision of flow control, this study develops a risk assessment method for offshore riser systems based on the characteristic parameters of riser outlet signals, achieving an identification accuracy exceeding 90% at different valve openings. Notably, the method maintains exceptional performance under high-pressure conditions, with identification accuracy reaching 96.74% at 10 MPa. On the other hand, this study focuses on the prediction of cut-off duration time in a cycle instead of the cycle period. We establish a predictive model for flow cut-off duration time under different choking conditions. Validation across diverse pipeline systems demonstrates strong reliability of the model, exhibiting maximum prediction errors of 30%. The model's coefficients can be fitted by a small dataset without significant loss of accuracy, and the coefficients are conservative, indicating strong applicability in the field operation. These findings offer significant theoretical insights and practical solutions for enhancing the operational safety of offshore oil and gas transportation systems. © 2025 Author(s).

关键词： Marine risers

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Hierarchical Heterojunctions of Metal Sulfide Nanosheets/ Metal Oxide Nanofibers for an Efficient Detection of Formaldehyde

SSRN

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SSRN 2024年

作者： Zhu, Lei Zhang, Jiaxin Wang, Jianan Liu, Jianwei Wang, Ze Yan, Wei Xi’an Key Laboratory of Solid Waste Resource Regeneration and Recycling State Key Laboratory of Multiphase Flow Engineering School of Energy and Power Engineering Xi’an Jiaotong University Xi’an710049 China School of Physics and Electrical Engineering Weinan Normal University Chaoyang Street Weinan714099 China School of Chemistry and Chemical Engineering Xi’an University of Science & Technology Xi’an710054 China

The construction of transition metal dichalcogenides (TMDs) heterojunctions for high performance gas sensors has garnered significant attention due to their capacity to operate at low temperature. Herein, we realize two-dimensional (2D) WS2 nanosheets in situ grown on one-dimensional (1D) In2O3 nanofibers to form heterostructures for formaldehyde (HCHO) gas sensors. Capitalizing on the p-n heterojunctions formed between WS2 and In2O3, coupled with the high surface-to-volume ratio characteristic of 1D nanostructures, the WS2/In2O3 NFs sensor demonstrated a high gas response value of 12.6 toward 100 ppm HCHO at operating temperature of 140 ℃, two times greater than that of the pristine In2O3 sensor. Meanwhile, the sensor presents remarkable repeatability, rapid response/ recovery time, and good long-term stability. The superior sensing capabilities of WS2/In2O3 NFs heterojunction are attributed to the combined impact of the increased charge transfer and the presence of more sites for gas adsorption. The research endows a potent approach for fabricating TMDs heterojunctions to significantly improve the performance of gas sensors. © 2024, The Authors. All rights reserved.

关键词： Tungsten compounds

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Microscopic characteristics study of liquid ammonia spray under different flash boiling conditions

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Fuel 2025年 401卷

作者： Xiao Liu Gangwei Zeng Xiaoxin Yao Chenglong Tang Zuohua Huang State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an 710049 China

Liquid ammonia, as a zero-carbon fuel, has received widespread attention in the field of internal combustion engines. The development of ammonia spray and evaporation models urgently requires accurate particle size distribution data. In this study, microscopic characteristics of liquid ammonia spray were firstly experimentally investigated under conditions of high injection pressure (up to 80 MPa) and ambient pressure (up to 4 MPa) with a single-hole injector (0.3 mm). Statistical results of microscopic parameters, including Sauter Mean Diameter (SMD), characteristic droplet diameter, and droplet number density were obtained over a wide range. The results indicate that ambient pressure or R P significantly affects the microscopic characteristics of ammonia spray. In flare flash boiling region (pressure ratio R P ≤ 0.3), ammonia spray produces more droplets with smaller diameter and the statistical SMD is around 15 μm. The droplet size increases and number density decreases with the increasement of ambient pressure or R P . In the transition flash (0.3 < R P ≤ 1) and non-flash boiling region ( R P > 1), the SMD statistical results are approximately 20 and 24 μm, respectively. Increasing the injection pressure can promote atomization and generate more smaller droplets, with a more uniform distribution. Ambient temperature slightly affects the microscopic characteristics of liquid ammonia spray within the temperature range selected for this study, but evaporation becomes more pronounced as the ambient temperature increases. The wide range droplet size distribution and SMD are believed to provide important data for ammonia spray modeling and simulation.

关键词： Internal combustion engines

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